Type I error rates from likelihood‐based repeated measures analyses of incomplete longitudinal data

The last observation carried forward (LOCF) approach is commonly utilized to handle missing values in the primary analysis of clinical trials. However, recent evidence suggests that likelihood‐based analyses developed under the missing at random (MAR) framework are sensible alternatives. The objective of this study was to assess the Type I error rates from a likelihood‐based MAR approach – mixed‐model repeated measures (MMRM) – compared with LOCF when estimating treatment contrasts for mean change from baseline to endpoint (Δ). Data emulating neuropsychiatric clinical trials were simulated in a 4 × 4 factorial arrangement of scenarios, using four patterns of mean changes over time and four strategies for deleting data to generate subject dropout via an MAR mechanism. In data with no dropout, estimates of Δ and SE_Δ from MMRM and LOCF were identical. In data with dropout, the Type I error rates (averaged across all scenarios) for MMRM and LOCF were 5.49% and 16.76%, respectively. In 11 of the 16 scenarios, the Type I error rate from MMRM was at least 1.00% closer to the expected rate of 5.00% than the corresponding rate from LOCF. In no scenario did LOCF yield a Type I error rate that was at least 1.00% closer to the expected rate than the corresponding rate from MMRM. The average estimate of SE_Δ from MMRM was greater in data with dropout than in complete data, whereas the average estimate of SE_Δ from LOCF was smaller in data with dropout than in complete data, suggesting that standard errors from MMRM better reflected the uncertainty in the data. The results from this investigation support those from previous studies, which found that MMRM provided reasonable control of Type I error even in the presence of MNAR missingness. No universally best approach to analysis of longitudinal data exists. However, likelihood‐based MAR approaches have been shown to perform well in a variety of situations and are a sensible alternative to the LOCF approach. MNAR methods can be used within a sensitivity analysis framework to test the potential presence and impact of MNAR data, thereby assessing robustness of results from an MAR method. Copyright © 2004 John Wiley & Sons, Ltd.     

职业地位取得的社会性别差异

本文从描述被调查夫妇之间职业流动的性别差异出发，分别勾画出他们的地位实现模型。首先验证了不论性别，教育地位都是决定职业地位实现的首要变量；但也正是在教育地位的实现和向上流动(再求学)中，伴随婚姻生育等生命事件的发生，无形的结构性制度因素(意识形态层面的性别制度、性别规范和性别文化)正如后现代主义试图解构的那样依然支配着性别角色的社会化和继续社会化，使扮演双重角色的妻子或无意识地或有意识地遭遇了丈夫不为之所累的两难困境，并最终阻碍了女性的教育地位、既而是职业地位的实现。本文最后提出了三点建议和几个尚待解决的问题。     

从《北回归线》看亨利·米勒的文体风格

亨利·米勒是美国20世纪的文学奇才,他的怪异文体使他备受针砭。《北回归线》不仅是他作品思想深度的代表作,也是其怪异文化的范本。以此为视点,米勒的文体风格主要可概括为卑琐素材、污秽物象、纵情声色、梦呓意识、拼贴构造等几个方面。     

The potential of integrated modelling in conservation biology: A case study of the black‐footed albatross (Phoebastria nigripes)

Conservation biology aims at assessing the status of a population, based on information which is often incomplete. Integrated population modelling based on state‐space models appears to be a powerful and relevant way of combining into a single likelihood several types of information such as capture‐recapture data and population surveys. In this paper, the authors describe the principles of integrated population modelling and they evaluate its performance for conservation biology based on a case study, that of the black‐footed albatross, a northern Pacific albatross species suspected to be impacted by longline fishing     

Parent‐Adolescent Communication About Sex: Retrospective Reports by Latino College Students

Latina female (n= 97) and Latino male (n= 69) college students (M age = 21.4 years) completed self‐report surveys regarding family of origin experiences, including sexual communication with parents while growing up. Latino parents of this comparatively highly educated sample tended to use direct rather than indirect strategies for communicating about sexuality with their children. Young women reported higher levels of sexual communication with mothers while growing up than did young men, and respondents reported less communication with fathers than mothers. Among young women, sexual communication with mother was positively associated with non‐Mexican origin and negatively associated with having older brothers living at home. In contrast, maternal education was positively associated with mother‐son communication about sex. Paternal education and the absence of older brothers positively predicted communication with both sons and daughters. The analyses provide novel information regarding sexual communication in Latino families and suggest directions for future research.     

Choice of the primary analysis in longitudinal clinical trials

Missing data, and the bias they can cause, are an almost ever‐present concern in clinical trials. The last observation carried forward (LOCF) approach has been frequently utilized to handle missing data in clinical trials, and is often specified in conjunction with analysis of variance (LOCF ANOVA) for the primary analysis. Considerable advances in statistical methodology, and in our ability to implement these methods, have been made in recent years. Likelihood‐based, mixed‐effects model approaches implemented under the missing at random (MAR) framework are now easy to implement, and are commonly used to analyse clinical trial data. Furthermore, such approaches are more robust to the biases from missing data, and provide better control of Type I and Type II errors than LOCF ANOVA. Empirical research and analytic proof have demonstrated that the behaviour of LOCF is uncertain, and in many situations it has not been conservative. Using LOCF as a composite measure of safety, tolerability and efficacy can lead to erroneous conclusions regarding the effectiveness of a drug. This approach also violates the fundamental basis of statistics as it involves testing an outcome that is not a physical parameter of the population, but rather a quantity that can be influenced by investigator behaviour, trial design, etc. Practice should shift away from using LOCF ANOVA as the primary analysis and focus on likelihood‐based, mixed‐effects model approaches developed under the MAR framework, with missing not at random methods used to assess robustness of the primary analysis. Copyright © 2004 John Wiley & Sons, Ltd.     

论儒家文化对东北婚俗的影响

几千年来,我国东北地区少数民族不断地兴衰更替,在中原占统治地位的儒家文化却不断向东北地区传播与渗透。儒家文化在东北地区却不断地为历代统治者所接纳,从而对东北的民俗不断地产生影响。就婚俗而言,从汉代《仪礼.士昏礼》的“六礼”传入东北,至晚清时期仍然保持着“六礼”形态,这是儒家礼仪文化自汉代以来在东北地区不断传播的结果。我们看到儒家文化生命力的同时,也看到在儒家文化影响下东北婚姻民俗所呈现的多彩的形态。     

数控机床功能的扩展

本文主要分析了HEIDENHAIN TNC 310数控铣床系统中圆弧铣削指令及螺纹铣削指令,对螺纹铣削功能进行延伸,扩展到圆弧三轴联动,并对螺纹铣削指令格式进行了修改,从而具有圆弧三轴联动铣削功能。     

北方方言中亲属称谓的"同形异指"现象初探

以《普通话基础方言基本词汇集》中的词汇材料为参考,从变调别义、轻声别义、元音变化别义、辅音变化别义以及词根变化别义几个方面对“同形异指”现象在亲属称谓中的表现加以分类考察,并探讨其本质。认为同一方言内部可以通过亲属称谓词语音单位的局部变化来区别易混淆的亲属称谓。     

从《马桥词典》看韩少功的语言风格

通过随机抽取的语例分析,可见韩少功《马桥词典》的语言风格,具有“乡”气扑鼻的朴实美,同构连用的繁丰美,而这些特点的形成,与作者的社会阅历和文化接受有关。